An adhesive material has been used for repairing/curing a wetting material containing moisture (hereinafter simply referred to as a “wetting material”) such as a biological hard tissue of a tooth, a bone or the like. As the adhesive material used for a wetting material, a resin-based curable composition including a radical monomer, a polymerization initiator and the like is widely used.
With respect to the resin-based curable composition, roughly divided two kinds of proposals have been conventionally made for improving the adhesiveness to a wetting material and to a biological hard tissue in particular. Specifically, one of the proposals is made with regard to a radical monomer including an acidic group with the intention of improving the chemical/physical interaction with a matrix of a tooth, a bone or the like to be adhered (see, for example, Patent Document 1), and the other proposal is made with regard to a polymerization initiator with the intention of efficiently polymerically curing, on a biological hard tissue, a curable composition including a radical monomer having an acidic group (see, for example, Patent Document 2).
When a resin-based curable composition is adhered onto a wetting material, sufficient bond strength cannot be attained in many cases because of curing inhibition caused by oxygen present on the adhesion interface. Such curing inhibition is caused seriously particularly when a curable composition is adhered onto dentin of a tooth or a bone including a large amount of oxygen.
Therefore, in order to accelerate the polymerization curing reaction while suppressing the curing inhibition derived from oxygen included in a wetting material, use of a redox polymerization initiator including a catalyst (an oxidizing agent) and an accelerator (a reducing agent) has been proposed. As the accelerator, a reducing compound including sulfur is regarded particularly promising (see, for example, Patent Documents 3 and 4).
Patent Document 3 proposes a redox-curing type aqueous polymeric composition composed of a first part including water-containing ethanol, sulfite, tertiary amine and the like and a second part including a free radical liquid monomer and a catalyst. Also, Patent Document 4 proposes a redox-curing type aqueous dental adhesive composition composed of a first part including a polymeric phosphorus compound, a polymerization catalyst and a diluent, a second part including aqueous ethanol, a sulfur compound and tertiary amine and a third part including aqueous ethanol and a soluble metal salt such as FeCl3. Such a divided redox-curing type aqueous curable composition is used with the divided parts mixed into one mixture before use.
The redox-curing type aqueous curable compositions described in Patent Documents 3 and 4 have, however, an antinomic problem. Specifically, when the amount of the accelerator such as sulfite or tertiary amine is increased for increasing the bond strength to a wetting material, the redox reaction (the oxidation-reduction reaction) is so rapidly proceeded that the working time is extremely too short for practical use. On the contrary, when the amount of the accelerator is reduced for securing a time necessary for an adhesion operation, sufficient curing cannot be attained and the bond strength to a wetting material is low.
It is a redox-curing type nonaqueous curable composition described in Patent Document 5 that overcomes the aforementioned antinomic problem of the redox-curing type aqueous curable compositions described in Patent Documents 3 and 4. The redox-curing type nonaqueous curable composition includes a liquid radical monomer, an organic peroxide and a powdered water-soluble reducing compound with the powdered water-soluble reducing compound dispersed in the liquid radical monomer. Specific examples of the powdered water-soluble reducing compound are described as powders of sulfite, hydrogensulfite, pyrosulfite, thiosulfite, thionate and dithionite (see Patent Document 5, paragraph [0038]). According to the description of Patent Document 5, polymerization inhibition caused by oxygen included in a wetting material is a phenomenon occurring not within a curable composition but on an adhesion interface between the curable composition and the wetting material, and therefore, when the aforementioned composition is employed, the redox reaction can be selectively accelerated merely on the adhesion interface where the polymerization inhibition is caused, resulting in improving the bond strength to the wetting material without largely reducing the working time.
Patent Document 1: Japanese Laid-Open Patent Publication No. 53-67740
Patent Document 2: Japanese Laid-Open Patent Publication No. 45-29195
Patent Document 3: Japanese Laid-Open Patent Publication No. 57-168903
Patent Document 4: Japanese Laid-Open Patent Publication No. 58-125710
Patent Document 5: WO2006/016545